The National Sleep Foundation (NSF), along with scientists from multiple disciplines, on Nov 6 announced a consensus on the threshold for when motorists are definitely too tired to drive. The conclusion: Drivers who have slept for two hours or less in the preceding 24 hours are not fit to operate a motor vehicle.

“Sleep is a fundamental physiological need that no human can avoid,” says NSF Drowsy Driving Consensus Workgroup Chair, Charles A. Czeisler, PhD, MD, FRCP, FAPS, in a release. Czeisler is also chief of the Division of Sleep and Circadian Disorders at the Brigham and Women’s Hospital and the Baldino Professor of Sleep Medicine at the Harvard Medical School. “While individual sleep needs vary, and stimulants, like caffeine, may trick sleep-deprived people into feeling alert, the reality is that people are definitely impaired when they have obtained two hours of sleep or less per day. Though many are impaired with more than twice as much sleep, at a minimum, our two-hour threshold should serve as a red flag warning for individuals and as a guide for public policy makers.”

David Cloud, NSF CEO, says, “Drowsy driving, like distracted and drunk driving, results in tragic yet preventable loss of more than 6,000 lives each year. We hope the work of the scientific community will inspire public policy makers, corporations and drivers to take action.”

The NSF convened experts from sleep, transportation, and medicine to reach a consensus on the definition. The definition is the result of a systematic literature review, followed by consensus building and voting.

The drowsy driving definition was announced during Drowsy Driving Prevention Week (November 1-6), a campaign to educate the public about the risks of drowsy driving and to improve safety on the road. The NSF is also focusing its annual conference, Sleep Health & Safety, on drowsy driving. Leaders in the sleep community, auto manufacturers, policy makers, and others are convened to discuss future autonomous driving features in new cars and the sleep related benefits and challenges presented by this technology.